1. Field of the Invention
This invention lies in the field of art relating to a lubricating oil composition adapted for use between a plurality of moving surfaces with which the fluid composition is in contact for the purpose of reducing the friction between these surfaces and to provide protection from wear and corrosion. These lubricant compositions tend to deteriorate under conditions of use with the attendant formation of sludge, lacquer and carbonaceous or resinous materials which adhere to the engine parts, particularly the piston rings, grooves and skirts, and cylinder walls thus reducing the operating efficiency of the engine. To counteract the formation of these deposits, and/or to ameliorate the effects of such deposits, certain chemical additives have been found, which when added to a lubricating oil, have the ability to minimize the formation of the deposits or to maintain the deposits formed suspended in the oil so that the engine is kept clean and in efficient operating condition for extended periods of time. These agents are known in the art to which this invention pertains as detergents, dispersants or detergent-dispersants. Metal organic compounds are particularly useful in this respect and are exemplified by the oil-soluble zinc, calcium and barium salts of petroleum sulfonic acids, alkylated hydroxy benzoic acids, dialkyl dithiophosphoric acids and the like.
There are drawbacks associated with the use of organic metal salts in a lubricating oil composition for an internal combustion engine. A major drawback is that the metal salts formed by neutralization of the acids resulting from the combustion process are generally insoluble in the lubricating oil composition. More importantly, these insoluble metal salts occur as hard deposits on the piston rings, piston skirts or the cylinder liners and in the ring grooves of the engine. These hard deposits are believed to be a major contributor to the wear that is experienced in an internal combustion engine. This problem is particularly acute with compression ignition engines, such as diesel engines, wherein the engine oil is subjected to extremely high temperature and compression stresses.
This invention also pertains to a method for lubricating an internal combustion engine which comprises supplying to the lubricating system of said engine the novel lubricating oil composition described hereinabove.
The novel lubricant and method of lubricating of this invention is most efficacious when employed in a compression ignition engine, such as a diesel engine, wherein the lubricating oil composition is subjected to extreme temperature and compression stresses including engine oil temperatures above about 600.degree. F which conditions are particularly prone to promote the formation of hard engine deposits.
2. Description of the Prior Art
The use of metal organic salts in a crankcase engine oil is disclosed in U.S. Pat. Nos. 3,528,917, 3,761,414, 3,969,235, 3,474,035 and 3,706,632. These disclosures are incorporated in the disclosure of this application.
U.S. Pat. No. 3,796,663 discloses a lubricating oil composition containing an N-hydroxy hydrocarbyl-substituted cyclic imide of a C.sub.4 -C.sub.5 dicarboxylic acid which is a multi-functional additive designed to inhibit rust, reduce wear and control friction on metallic surfaces.